System for contactless power transfer between nacelle and tower of a windturbine

ABSTRACT

The present invention relates to a transformer ( 100 ) for the transfer of electrical power from a nacelle ( 250 ) of a horizontal-axis wind turbine to a turbine tower ( 350 ) of said wind turbine whereby the nacelle ( 250 ) is in revolute attachment to the tower ( 350 ), comprising: a primary winding ( 200 ) adapted for attachment to the nacelle ( 250 ), and a secondary winding ( 300 ) adapted for attachment to the turbine tower ( 350 ), which windings ( 200, 300 ) are in revolute alignment with each other, and configured for transfer of electrical power by induction from the primary winding ( 200 ) to the secondary winding ( 300 ). It also relates to a method for assembly or disassembly of a wind turbine.

FIELD OF THE INVENTION

The present invention is in the field of wind turbines. More in particular, it is in the field of power transfer between a wind turbine nacelle and tower on which the nacelle is mounted revolutely.

BACKGROUND TO THE INVENTION

The nacelle of a wind turbine is typically suspended at the top of a tower in horizontal axis systems using a rotating (revolute) mounting. The power produced by the generator in the nacelle needs to be transferred to the base of the tower. For larger turbines this is usually achieved using a cable connected to the nacelle which passes through a passageway disposed within the tower. Slack in the cable towards the upper part of the tower allows for some degree of cable coiling due to rotation (yawing) of the nacelle that follows any change in wind direction. A device counting the number of turns is used to limit the maximum coiling of the cable. Once this maximum has been reached, the turbine is stopped and a yaw mechanism unwinds the cable by rotating the nacelle in the opposite direction of the coiling, thereby restoring the cable to its original unwound condition.

The system of the art is associated with several disadvantages. Additional cable must be foreseen to allow for the coiling, which adds to the expense of construction. The cable is suspended through the aforementioned passageway using a net made of steel cable; as the conducting cable is made from thick copper, and is quite heavy, large forces are applied to the net, often leading to fatigue and failure. The system needs a mechanism to count the number of turns that the cable has been coiled; such a mechanism requires maintenance and provides a potential source of failure and expense. The system also requires an active yaw mechanism to unwind the cable once the maximum allowed number of turns has been reached; again this mechanism requires maintenance and provides a potential source of failure and expense. Cable damage and eventually short-circuits cause by failure of these systems lead to additional expense. Downtime, while the turbine blade is stopped and the nacelle rotated, leads to a loss of production and is significant at sites where wind direction is variable.

Smaller turbines (e.g. below 50 kW rated power) sometimes employ slip-ring units to transfer the power from the rotating nacelle to the fixed tower. A slip ring unit consists of a set of brushes and a set of rings that form rotating contacts. Uniformly distributed pressure for a contact between the brush and the ring is usually assured using springs. This system has numerous disadvantages. Dependent upon the yaw rate and the amount of current transferred, the brushes, usually made out of carbon, wear down regularly and need to be replaced, which contributes to running costs which includes downtime. The slip-ring unit needs to be mounted so that the alignment between the brushes and the contact rings is correct, to avoid that the brushes wear unduly; this alignment process requires time and specialist equipment. The slip ring assembly generates carbon dust caused by wearing of the brushes; therefore an evaluation system is required to prevent short-circuits caused by the conductive carbon; such a system requires maintenance and provides a potential source of failure and expense.

Contact-less power transmission is a generally known method used in mechanical and electrical engineering fields with particular use in consumer devices. In U.S. Pat. No. 7,622,891 (Cheng et al., Nov. 24 2010) a general device is described to inductively power a secondary unit. The device eases manipulation for the user as it is not necessary to place the power-receiving unit in mechanical or other registration with the power-transmitting device. U.S. Pat. No. 7,717,619 (Karch et al., May 18 2010) describes contactless data transmission for CT imaging purposes. US 2007/0007857 (Cullen et al., Jan. 11 2007) describes a wind-turbine architecture eliminating the problem of slip-rings and cable wind-up.

SUMMARY OF THE INVENTION

The present invention is a system for contactless, (zero-wear) power transfer from a wind turbine nacelle to a wind turbine tower on which the nacelle is attached. The nacelle is preferably a horizontal axis system i.e. the axle of the turbine blades is aligned essentially horizontally. The wind turbine tower is preferably longitudinal, and vertically mounted. The wind turbine nacelle is attached to a wind turbine tower using a revolute (rotatable or yawing) mounting. The tower may be fixed to the ground or to the seabed, or be floating on water.

In general the tower is not able to rotate around its longitudinal axis, while the nacelle is able to rotate around the longitudinal axis of the tower in order to track the wind direction and keep the rotor perpendicular to the dominating wind flow. The relative motion between the nacelle and the tower is known as the yawing or yaw motion, and is in most cases facilitated by a yaw bearing. The power generated by the wind turbine electrical generator thus has to be transmitted from the rotating nacelle that is connected to the fixed tower.

One aspect provides a transformer comprising a primary winding and secondary winding arranged in concentric alignment. The primary winding is configured for attachment to the nacelle; the secondary winding is configured for attachment to the turbine tower. The secondary winding and the primary winding are also in rotatable (revolute) alignment. In the wind turbine, the primary windings in the tower and the secondary windings in the nacelle align such that they form a transformer.

Alternating current (AC) provided by the generator housed in the nacelle is transferred wirelessly via the transformer to the tower, without the need for an arrangement of slip-rings or a direct cable connection. The operation of the transformer is such that it is independent of the relative (revolute) orientation of the primary and secondary windings. The nacelle can thus rotate freely and track the wind direction without having to take into account its rotational position in relation with the tower. On other words, the system permits an infinite number of turns. This invention is thus particularly well suited in combination with a free yaw system where there is no active system controlling the yaw motion but rather the aerodynamic forces are used to ensure proper orientation of the nacelle in the wind flow.

The generator housed in the nacelle may supply alternating current at a fixed-frequency. The generator housed in the nacelle may supply alternating current at a variable-frequency. The transformer will wireless transfer power to the tower, regardless of the frequency of the alternating current. It will be appreciated that higher alternating current output frequencies allow for a more compact transformer. One aspect provides a power converter for transforming the low-frequency alternating current provided by the generator into a higher-frequency current, for instance in the kHz range (e.g. at least 1 kHz, 10 kHz, 50 kHz, 100 kHz or a value in the range between any two of the aforementioned values). This would reduce the size and thus the weight of the rotating transformer arrangement thereby reducing costs.

Cables connected to the primary winding conduct power generated by the wind tower to an electrical collector network of a wind farm or to a grid, optionally via one or more power converters.

The invention does not add any unnecessary components to the conversion process of a wind turbine. Turbines with rated powers starting at several hundreds of kilowatts are usually connected to the distribution grid and thus use step-up transformers to convert the lower output voltage of the generator to the voltage level of the grid. In turbines that have tall towers, it is commonplace to do this transformation in the nacelle to limit the conduction losses in the cables that descend from the tower. Such modern-day turbines already include a Low-voltage-to-Medium-voltage transformer in the nacelle. Hence the invention does not add any or significant weight to the tower-top mass (the total mass of the turbine placed on top of the tower). In addition may make the nacelle more compact as transformer can now be integrated in the tower top, as opposed to occupying space within the nacelle.

One aspect of the invention relates to a transformer (100) for the transfer of electrical power from a nacelle (250) of a horizontal-axis wind turbine to a turbine tower (350) of said wind turbine whereby the nacelle (250) is in revolute attachment to the tower (350), comprising:

-   -   a primary winding (200) adapted for attachment to the nacelle         (250), and     -   a secondary winding (300) adapted for attachment to the turbine         tower (350),         which windings (200, 300) are in revolute alignment with each         other, and configured for transfer of electrical power by         induction from the primary winding (200) to the secondary         winding (300).

The primary (200) and secondary (300) windings may be in essentially concentric alignment. The primary (200) winding may be outside of the secondary (300) winding. The primary winding (200) may comprise an annular inductive coil (210) and an annular magnetically permeable member (220, 222), whereby the annular magnetically permeable member (222) is disposed around the outside of the coil (210). The secondary winding (300) may comprise an annular inductive coil (310) and a cylindrical magnetically permeable member (320, 322), whereby the coil (310) is disposed around the outside of the cylindrical magnetically permeable member (322). The secondary (300) winding may be outside of the primary (200) winding. The transformer (100) may be configured for inductive transfer of high-frequency alternating current.

Another aspect of the invention relates to a horizontal-axis wind turbine comprising turbine tower (350) and a nacelle (250) in revolute attachment to the tower (350), comprising a transformer (100) describe herein. The revolute attachment may comprise a mounting (150) into which the transformer (100) is integrated. The mounting (150) may comprise a nacelle part (230) and a tower part (330) that couple together, and the primary (200) winding is integrated into the nacelle part (230) and the secondary (300) winding is integrated into the tower part (330).

One of said mounting parts (230, 330) may comprise a cylindrical pin, the other of said mounting parts may comprise a cylindrical cavity configured to slidably receive the cylindrical pin. Said turbine tower (350) may be at least partially hollow. Said nacelle (250) may be dismountably attached to the tower (350).

Another aspect of the invention relates to a method of assembling a horizontal-axis wind turbine as described herein, comprising the steps:

-   -   installing the wind turbine tower (350) comprising a secondary         winding (300) on a site, and     -   mounting the nacelle (250) comprising a primary winding (200) on         said tower (350), such that primary winding (200) and said         secondary winding (300) form the transformer (100) when said         nacelle and said tower are assembled.

Another aspect of the invention relates to a method of assembling a horizontal-axis wind turbine as described herein comprising the step of lifting the nacelle comprising a primary winding (200) from the wind turbine tower comprising the secondary winding (300).

FIGURE LEGENDS

FIG. 1 is a schematic perspective view of a transformer described herein.

FIG. 2 is a cross sectional view through a plane parallel and adjacent to the central axis of the transformer. Hatched shading indicates magnetically permeable material while horizontal shading indicates inductive coil.

FIG. 3 is a cross sectional view through a plane parallel and adjacent to the central axis of the tower. One transformer is shown.

FIG. 4 is a cross sectional view through a plane parallel and adjacent to the central axis of the tower. Three transformers are shown.

FIG. 5 is a cross sectional view through a plane parallel and adjacent to the central axis of the tower. Three transformers are shown that are magnetically coupled.

DETAILED DESCRIPTION OF THE INVENTION

Before the present system and method of the invention are described, it is to be understood that this invention is not limited to particular systems and methods or combinations described, since such systems and methods and combinations may, of course, vary. It is also to be understood that the terminology used herein is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

As used herein, the singular forms “a”, “an”, and “the” include both singular and plural referents unless the context clearly dictates otherwise.

The terms “comprising”, “comprises” and “comprised of” as used herein are synonymous with “including”, “includes” or “containing”, “contains”, and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms “comprising”, “comprises” and “comprised of” as used herein comprise the terms “consisting of”, “consists” and “consists of”.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

Whereas the terms “one or more” or “at least one”, such as one or more or at least one member(s) of a group of members, is clear per se, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or to any two or more of said members, such as, e.g., any ≧3, ≧4, ≧5, ≧6, or 24 7 etc. of said members, and up to all said members.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

In the following passages, different aspects of the invention are defined in more detail. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration only of specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilised and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

With reference to FIG. 1, one aspect of the invention relates to a transformer 100, (rotating transformer), for the transfer of electrical power from a nacelle of a horizontal-axis wind turbine to a turbine tower of said wind turbine, whereby the nacelle is in revolute attachment to the tower, comprising a primary winding 200 adapted for attachment to the nacelle and a secondary winding 300 adapted for attachment to the tower which windings 200, 300 are revolute (rotatable) and optionally in essentially concentric alignment with each other, configured for transfer of electrical power by induction from the primary winding 200 to the secondary winding 300. The rotation is about an axis of rotation R-R′. One winding is generally static, while the other winding rotates around that axis of rotation. In FIGS. 1 to 3, the primary winding 200 is on the outside and rotates, while the secondary winding 300 is on the inside and is static relative to the primary winding 200. It will be appreciated that other configurations are possible e.g. the primary winding 200 may be on the inside. The primary winding 200, the secondary winding 300 or both windings 200, 300 may incorporate one or more magnetically permeable members (e.g. core) such as iron for guidance of the flux, particularly across an annular air gap between the primary 200 and secondary 300 windings.

With reference to FIGS. 2 and 3, the primary winding 200 comprises a primary winding inductive coil 210 that is electrically connected directly or indirectly to the generator housed in the nacelle. The primary winding coil 210 preferably forms an annular (circular) ring, having a central axis. The central (A-A′) axis of the coil 210 is essentially co-axial with the axis of rotation of the transformer 100. The primary winding 200 may further comprise at least one magnetically permeable member 220, having a cylindrical or annular shape 222 and having a central axis. The central axis of the magnetically permeable member 222 is essentially co-axial with the axis of rotation of the transformer. The coil 210 and magnetically permeable member 222 are preferable in concentric and optionally co-axial alignment. The coil 210 may be made from copper or aluminum formed into wire or foil. It may be form-wound for higher power ratings. The primary winding 200 is in fixed relation to the nacelle 250, and thus rotates as the nacelle 250 rotates around the longitudinal axis of the tower 350.

With reference to FIGS. 2 and 3, the secondary winding 300 comprises an inductive coil 310 that is electrically connected to the output of the wind tower located in the wind tower. The secondary winding coil 310 preferably forms an annular (circular) ring, having a central axis. The central (A-A′) axis of the coil 310 is essentially co-axial with the axis of rotation of the transformer 100. The secondary winding 300 may further comprise at least one magnetically permeable member 320, having a cylindrical or annular shape and having a central axis. The central axis is essentially co-axial with the axis of rotation of the transformer 100. The secondary winding coil 310 and magnetically permeable member 320 are preferable in concentric and optionally co-axial alignment. The coil 310 may be made from copper or aluminum formed into wire or foil. It may be form-wound for higher power ratings. The secondary winding 300 is in fixed relation to the tower, and thus stationary.

The primary 200 and secondary 300 windings are preferably in essentially concentric alignment. In this arrangement, the primary winding 200 (the outer winding) may be disposed around the outside of the secondary winding 300 (the inner winding) as illustrated in FIG. 2. Alternatively, the secondary winding 300 (the outer winding) may be disposed around the outside of the primary winding 200 (the inner winding) (not illustrated). The arrangement will depend on the configuration of the rotatable mounting used to attach the nacelle 250 to the tower 350. Generally, the primary winding 200 is integrated into the one part of the mounting and the secondary winding 300 is integrated into the another reciprocating part of the mounting, such that the primary 200 and secondary windings 300 are in concentric (overlapping) alignment when the nacelle 250 is mounted on the tower 300.

As mentioned elsewhere, the primary winding 200, the secondary winding 300 or both windings may incorporate an arrangement of one or more of magnetically permeable members 230, 320, made, for instance from iron for conductance of the flux, particularly across an air gap between the primary and secondary winding. A magnetically permeable member (sometimes known as a core) is made from magnetically conductive material. It provides a path of minimum resistance to magnetic flux generated by the coil. A magnetically permeable member may be made from any high permeability magnetically conductive material. In one example, a magnetically permeable member may be made from iron. Preferably a magnetically permeable member is made from non-grain oriented iron to reduce the weigh of the transformer and to reduce the losses. Depending on the function of the transformer, frequency and its rated power, other materials such as ferrites or iron powder may be used.

According to one aspect, magnetically permeable members 220, 320 are arranged to give rise to a shell-type transformer. In a shell-type transformer, the outer winding comprising an annular cylinder of magnetically permeable material 220, 320 that encloses the coil of the outer winding, and the coil is flanked by a pair of end plates of magnetically permeable material. The central axis (A-A′) of annular ring of magnetically permeable material is essentially co-axial with the axis of rotation of the transformer. Exemplified in FIG. 2, the primary winding 200 is on the outside and comprises an annular cylinder 222 of magnetically permeable material that encloses the coil 210, and the coil 210 is flanked by a pair of end plates 224, 226 of magnetically permeable material. The shell-type transformer has the advantage that no coil is apparent outside the permeable members. The magnetically permeable material encloses the coil, which provides robustness to short circuit and transportation efforts, and compactness of the design to match transportation and hauling restrictions. It is appreciated that magnetically permeable members may be arranged to give rise to a core-type transformer in the outer winding i.e. the coil of the outer winding is arranged around an annular ring of magnetically permeable material.

In a standard transformer, the amount of magnetic flux passing through each of the primary and secondary windings is similar or the same by disposing both windings on the same continuous magnetically permeable member (core). In the present case, the magnetically permeable members 220, 320 are arranged in a discontinuous manner, i.e. there is an air gap between magnetically permeable members (core) of the primary 200 and secondary 300 windings of the transformer in order to allow for relative rotational movement. The air gap in between the inner and outer part of the magnetic core is minimised in order to limit the leakage inductance of the transformer. In FIG. 2 the air gap 160 between the primary 200 and secondary 300 windings has an annular cylindrical shape.

According to one aspect, magnetically permeable members 220, 320 are arranged to give rise to a reel shape, around which reel the coil is wound. The reel has a cylindrical core 322 that is flanked by a pair of disc-shaped end plates 324, 326. The central axis of the reel is essentially co-axial with an axis of the rotation of the transformer. In FIG. 2, the a secondary winding 300 is an inner winding, and which the magnetically permeable members 320 are arranged to give rise to said reel shape, around which reel the coil 310 is wound.

A cylindrical magnetically permeable member of the inner winding of a transformer may comprise one or more longitudinal grooves on the surface for the passage of conductive wires from transformers located above to grid interconnection at the base of the tower. Preferably, three longitudinal grooves are evenly arranged around the cylindrical surface of the magnetically permeable member. In other words, they are circumferentially distributed at intervals of 120 deg. Where there are three transformers in a wind turbine, the grooves may be offset in order to have a balance in magnetic forces in all relative positions of the primary and secondary windings and thus no preferred positions. It will be appreciated that the groove arrangement may be achieved using three segments of magnetically permeable material which together form essentially a cylindrical shape.

The magnetically permeable members can be prolonged to be in contact with the outer surface of the tower in order to have a better cooling and/or to fit with the mechanical support structure.

As mentioned elsewhere herein, the coil 210, 310 of one or both windings may be made from a foil. In other words, from an insulated strip of conductive metal, as opposed from a conventional strand of wire. A foil coil can be used with some advantage. For instance, with respect to the inner winding, a foil can be easily wound around magnetically permeable member when it forms the shape of a reel, as shown in FIG. 2. A polyester layer is bonded to the foil to provide mechanical strength and for insulation.

With respect to the outer winding, a foil coil can form a ring onto which the segments of annular magnetically permeable member can be fitted. The conductive metal may be a flat strip. For high voltage, rectangular conducting strips are preferred.

As mentioned earlier, the nacelle 250 is in revolute attachment to the tower 350 using a rotatable (revolute) mounting 150. As the invention allows for relative rotation of the primary 200 and secondary 300 windings of the transformer 100, the mounting is configured for integration of the transformer components, namely these primary and secondary windings. The windings may be integrated into the mounting 150 by virtue of a mechanical support structure. The mounting preferably comprising a bearing that transfer the weight of the nacelle onto the wind tower while allowing yawing

With reference to FIG. 3, the mounting 150 may comprise a nacelle part 230 and a tower part 330, one of said mounting parts comprising a cylindrical pin, the other of said mounting parts comprising a cylindrical cavity configured to slidably receive the cylindrical pin. In other words, the pin and cylindrical cavity are in slidable relation. In FIG. 3, the nacelle part 320 of the mounting comprises a cylindrical cavity while the tower part 330 comprises the cylindrical pin. It is understood that other configurations are possible, for instance, the nacelle part 320 of the mounting may comprise a cylindrical pin while the tower part 330 may comprise the cylindrical cavity. According to one aspect, the nacelle 250 is dismountably attached to the tower 350. According to another aspect, the nacelle part 320 is dismountably attached to the tower part 330 of the mounting. A dismountable attachment is configured for reversible attachment (e.g. for ease of attachment and unattachment) of the respective elements.

The primary winding 200 is integrated into the nacelle part 230 of the mounting 150. Preferably it is integrated so that the outer cylindrical profile is maintained. The secondary winding 300 is integrated into the tower part 330 of the mounting 150. Preferably it is integrated so that the outer cylindrical profile is maintained. The primary 200 and secondary 300 windings may each be disposed in a housing configured to withstand the bending loads due to the aerodynamic forces and gravity.

One or more yaw bearings 170, 175 (FIG. 3) may be provided where the nacelle part 230 and a tower part 330 of the mounting are in mechanical contact, preferably where the weight of the nacelle 250 is supported by the tower 350. Typically they are provided at the longitudinal end of the cylindrical pin (see bearing 170) and around the mouth of the cylindrical cavity (see bearing 175). The former bearing may assure the exact spacing between the two parts of the rotating transformer. The yaw bearing may be a sliding or rolling bearing.

A wind turbine may be provided with one or more (e.g. 2, 3, 4 or more) transformers 100. FIG. 4 depicts a wind turbine disposed with three separate transformers 100, 100′ 100″, one for each phase. Also shown is the nacelle 250 and turbine blades 252 and wind tower 350.The transformers are arranged in longitudinal displacement along the mounting. Their central axes are preferably essentially co-axial. The transformers are preferably spatially separated from each other. Where there are two or more transformers, they may be arranged adjacently i.e. without air gaps in the longitudinal direction, so that at least some of the flux circuits of one transformer pass through an adjacent transformer. More in particular, at least some of the flux conducted by the magnetically permeable members of one transformer extends through magnetically permeable members of adjacent transformers. By magnetically coupling the transformers so, the number of magnetically permeable members may be reduced, thus allowing a more compact mounting and, therefore, facilitating a more economically produced wind turbine. FIG. 5 depicts a wind turbine disposed with three separate transformers 100, 100′ 100″, one for each phase, arranged in the longitudinal direction without air gaps between adjacent magnetically permeable members 224, 226, 324, 326 in the longitudinal direction.

Another aspect described is the horizontal-axis wind turbine described herein comprising the turbine tower 350 and a nacelle 250 in revolute attachment to the tower 350, comprising the transformer 100 as described herein. The revolute attachment may comprise the mounting 150 into which the transformer 100 is integrated. The mounting 150 may comprise a nacelle part 230 and a tower part 330 that couple together, and the primary 200 winding may be integrated into the nacelle part 230 and the secondary 300 winding may be integrated into the tower part 330. One of said mounting parts 230, 330 may comprise a cylindrical pin, the other of said mounting parts comprising a cylindrical cavity configured to slidably receive the cylindrical pin. The turbine tower 350 may be at least partially hollow. The nacelle 250 may be dismountably attached to the tower 350.

The above described transformer 100 and system would be suitable for a three-phase 100 kW wind turbine and may have a capacity of 105 kVA. The system is not necessarily limited to the aforementioned parameters. The invention is applicable over a range of wind turbine rated powers from small (e.g. several hundreds of watts) turbines to very large (e.g. tens of MW's) turbines.

The present invention allows for easy removal of the nacelle 250 from a tower 350 that is fixed to the ground, the seabed or floating in sea. A lifting device (crane or even a helicopter) removes the complete nacelle structure 250 and separate primary 200 and secondary 300 side of the transformer 100 by lifting the nacelle 250 vertically. By making both sides of the mounting completely enclosed and weather resistant, the tower 350 together with the secondary winding 350 of the transformer 150 may be left in place for indefinite time while the nacelle 250, and the primary winding 200 of the transformer 100, undergo maintenance. Repairs may be performed by replacing a complete nacelle 250 to ensure rapid resuming of power production while the faulty nacelle 250 is being investigated and repaired onshore.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. 

1. A horizontal-axis wind turbine comprising turbine tower (350) and a nacelle (250) in revolute attachment to the tower (350), comprising a transformer (100) for the transfer of electrical power from the nacelle (250) to the turbine tower (350), which transformer comprises: a primary winding (200) adapted for attachment to the nacelle (250), and a secondary winding (300) adapted for attachment to the turbine tower (350), which windings (200, 300) are in revolute alignment with each other, and configured for transfer of electrical power by induction from the primary winding (200) to the secondary winding (300), wherein the revolute attachment comprises a mounting (150) into which the transformer (100) is integrated, which mounting comprises a nacelle part (230) and a tower part (330) that couple together, and the primary (200) winding is integrated into the nacelle part (230) and the secondary (300) winding is integrated into the tower part (330). wherein one of said mounting parts (230, 330) comprising a cylindrical pin, the other of said mounting parts comprising a cylindrical cavity configured to slidably receive the cylindrical pin.
 2. Horizontal-axis wind turbine according to claim 1, wherein the primary (200) and secondary (300) windings are in essentially concentric alignment.
 3. Horizontal-axis wind turbine according to claim 1, wherein the primary (200) winding is outside of the secondary (300) winding.
 4. Horizontal-axis wind turbine according to claim 3, wherein the primary winding (200) comprises an annular inductive coil (210) and an annular magnetically permeable member (220, 222), whereby the annular magnetically permeable member (222) is disposed around the outside of the coil (210).
 5. Horizontal-axis wind turbine according to claim 3 wherein the secondary winding (300) comprises an annular inductive coil (310) and a cylindrical magnetically permeable member (320, 322), whereby the coil (310) is disposed around the outside of the cylindrical magnetically permeable member (322).
 6. Horizontal-axis wind turbine according to claim 1, wherein the secondary (300) winding is outside of the primary (200) winding.
 7. Horizontal-axis wind turbine according to claim 1, wherein said turbine tower (350) is at least partially hollow.
 8. Horizontal-axis wind turbine according to claim 1, wherein said nacelle (250) is dismountably attached to the tower (350).
 9. A method of assembling a horizontal-axis wind turbine which horizontal-axis wind turbine comprising a turbine tower (350) and a nacelle (250) in revolute attachment to the tower (350), and a transformer (100) for the transfer of electrical power from the nacelle (250) to the turbine tower (350), which transformer comprises: a primary winding (200) adapted for attachment to the nacelle (250), and a secondary winding (300) adapted for attachment to the turbine tower (350), which windings (200, 300) are in revolute alignment with each other, and configured for transfer of electrical power by induction from the primary winding (200) to the secondary winding (300), comprising the steps: installing the wind turbine tower (350) comprising a secondary winding (300) on a site, and mounting the nacelle (250) comprising a primary winding (200) on said tower (350), such that primary winding (200) and said secondary winding (300) form the transformer (100) when said nacelle and said tower are assembled.
 10. A method of disassembling a horizontal-axis wind turbine which horizontal-axis wind turbine comprising a turbine tower (350) and a nacelle (250) in revolute attachment to the tower (350), and a transformer (100) for the transfer of electrical power from the nacelle (250) to the turbine tower (350), which transformer comprises: a primary winding (200) adapted for attachment to the nacelle (250), and a secondary winding (300) adapted for attachment to the turbine tower (350), which windings (200, 300) are in revolute alignment with each other, and configured for transfer of electrical power by induction from the primary winding (200) to the secondary winding (300), comprising the step of lifting the nacelle comprising a primary winding (200) from the wind turbine tower comprising the secondary winding (300).
 11. Method according to claim 9, wherein the primary (200) and secondary (300) windings are in essentially concentric alignment.
 12. Method according to claim 9, wherein the primary (200) winding is outside of the secondary (300) winding.
 13. Method according to claim 12, wherein the primary winding (200) comprises an annular inductive coil (210) and an annular magnetically permeable member (220, 222), whereby the annular magnetically permeable member (222) is disposed around the outside of the coil (210).
 14. Method according to claim 12, wherein the secondary winding (300) comprises an annular inductive coil (310) and a cylindrical magnetically permeable member (320, 322), whereby the coil (310) is disposed around the outside of the cylindrical magnetically permeable member (322).
 15. Method according to any claim 11, wherein the secondary (300) winding is outside of the primary (200) winding. 